Small random-orbit or pad sanders make this job go faster. (Wallis first covers these boundaries with Synkoloid patching compound so no edge is visible after sanding.) As shown, you want to make sure that there is a feathered, smooth transition from exposed wood to old paint. For areas that might get close scrutiny, you can follow up with a 100- or 120-grit rubdown to erase any scratches.
Every painting job develops a unique choreography as ladders go up and come down and tarps are unrolled and folded up. But two basic principles remain: 1) Start at the top and work down. 2) Work in the shade, out of the sun's glare. As the dance proceeds, keep an eye on the weather. Rain can wash freshly applied latex right off the wall, and a temperature dip below 50 degrees F two days after application can interfere with adhesion and curing and dull the sheen of glossy paints. (Latexes like Sherwin-Williams's Duration and Benjamin Moore's MoorGard Low Lustre are formulated to tolerate temps as low as 35 and 40 degrees, respectively.) House Painting